1. Field of the Invention
The present invention relates to a device which effects a feed-back control of the ignition timing or other suitable control variable of an engine by detecting the knocking produced in the engine.
2. Background of the Invention
In a general engine, it is known that a continuous strong knocking state adversely affects the durability of the engine while a relatively weak knocking state in the low revolution speed range of the engine provides optimum fuel consumption and engine power output characteristics. The occurence of knocking is a closely related to the ignition timing, and tends to be enhanced as the ignition timing is advanced.
Devices are known which maintains a weak knocking state by detecting the knocking state and advancing or retarding the ignition timing in response to the detected knocking state, in order to optimize the operating characteristics of the engine.
When a knocking state is detected in such a conventional device the ignition timing is actually regulated after a predetermined period which corresponds to the delay time in the response characteristic of the feed-back control system. Thus, for variations in the knocking state which are slow with regard to the predetermined period, the ignition timing can be positively controlled in an optimum manner.
In a transitional driving condition in which the driving condition changes suddenly, the knocking state also changes suddenly. However, the ignition timing cannot be controlled as quickly as desired in response to sudden variations of the knocking state due to the abovementioned delay time. Thus an optimum control of the ignition timing may not be effected during transitional driving conditions.
The knocking state tends to be enhanced during the transitional driving condition of acceleration of the vehicle therefore ignition timing should be retarded as quickly as possible. On the other hand, in order to stabilize the control or to prevent hunting, the ignition timing can only be retarded at a predetermined limited rate, and not as quickly as required. The result is an inability to control the ignition timing in an optimum manner during the sudden acceleration so that the combustion, fuel consumption and output power characteristics will show a marked tendency to deteriorate.